The field of the disclosure relates generally to ceramic slurry compositions, and more particularly to slurry compositions that include particle size and/or shape distributions that reduce total and differential shrinkage during a process of forming a ceramic article from the composition.
It is desirable to form at least some ceramic articles in a process that avoids shrinkage during firing of the ceramic article or during subsequent use of the article. For example, at least some metal components are formed in a casting process around a ceramic core, and it is desirable for cores to have low process shrinkages during firing of the core and/or casting of the component, typically 1.5 percent or less, to meet tight dimensional specifications for the finished metal component. Furthermore, it is desirable to reduce core cracking, which may be due to differential shrinkage between thick and thin sections in the core during firing and/or casting. Modifications, such as hollowing out thick sections in the starting die used to form the ceramic article, may be used to mitigate this shrinkage mismatch. However, such modifications require undesirable additional processing steps.
Reduction in total and differential shrinkage of the ceramic article is typically achieved by crystallization of amorphous silica during firing. The formation of the crystalline phase results in reduced viscous sintering of the silica amorphous phase. In addition, a threshold amount of crystalline silica phase (e.g., cristobalite, quartz, etc.) is required, for example, prior to casting in order to achieve subsequent cast metal blade dimensional tolerances.
One approach to inducing cristobalite formation is to include a dopant (i.e., a flux) in the slurry, which allows for formation of adequate cristobalite levels prior to use in, for example, investment casting of metal. Another approach is to use higher solids loading in the slurry. The higher solids loading may be used instead of, or in conjunction with, the use of a dopant. Higher solids loading also results in increased ceramic article strength. However, increasing higher solids loading of the slurry results in an increased viscosity of the slurry, which can cause damage to, for example, polymer-based core dies.